Carbohydrate-based polyesters made from bicyclic acetalized galactaric acid.

The dimethyl ester of 2,3:4,5-di-O-methylene-galactaric acid (Galx) was made to react in the melt with 1,n-alkanediols HO(CH(2))(n)OH containing even numbers of methylenes (n from 6 to 12) to produce linear polycyclic polyesters. Two sets of poly(alkylene 2,3:4,5-di-O-methylene-galactarate) polyesters (PE-nGalx) with weight-average molecular weights in the ∼ 5000-10000 and ∼ 35000-45000 ranges were obtained using TBT and DBTO catalysts, respectively. For comparative purposes a set of poly(alkylene adipate) polyesters (PE-nAd) was also synthesized with molecular weights in the higher range using a similar procedure. The thermal stability of PE-nGalx was greater than that of PE-nAd although it notably decayed as molecular weight decreased. The replacement of Ad by Galx in the polyesters caused increases in T(g) of up to 70 °C, and almost doubled the tensile mechanical parameters. All PE-nGalx were semicrystalline but only those made from 1,12-dodecanediol were able to crystallize from the melt with a crystallization rate that diminished as the molecular weight increased. In general, the galactarate containing polyesters displayed higher solubility and wettability than polyadipates, they hydrolyzed faster and exhibited comparable sensitivity to the action of lipases.

Synthetic polymers from readily available monosaccharides.

The low degradability of petroleum-based polymers and the massive use of these materials constitute a serious problem because of the environmental pollution that they can cause. Thus, sustained efforts have been extensively devoted to produce new polymers based on natural renewing resources and with higher degradability. Of the different natural sources, carbohydrates stand out as highly convenient raw materials because they are inexpensive, readily available, and provide great stereochemical diversity. New polymers, analogous to the more accredited technical polymers, but based on chiral monomers, have been synthesized from natural and available sugars. This chapter describes the potential of sugar-based monomers as precursors to a wide variety of macromolecular materials.

Synthesis and secondary structure of oligo(alpha-isobutyl beta,L-aspartate)s.

The oligo(beta-peptide)s, hexa(alpha-isobutyl beta,L-aspartate) (Hex-AIBLA) and octa(alpha-isobutyl beta,L-aspartate) (Oct-AIBLA), were synthesized in solution by using standard coupling methods. Powder x-ray diffraction showed that the octamer crystallized in the two helical crystal forms known to exist in the homologous poly(beta-peptide), whereas the hexamer seemed to adopt an extended conformation. Both CD and 1H-NMR spectra of Oct-AIBLA in MeOH revealed the presence of a regularly folded conformation in this solvent, presumably the 3(14) helix. The helix-to-coil transition of Oct-AIBLA was observed to take place upon heating in both MeOH and CHCl3, in the second case associated with a not-well-defined aggregation-disaggregation process. The spectroscopic evidence obtained on the presence of folded structures in Hex-AIBLA were much weaker than for the octamer.

Synthesis of L-arabinitol and xylitol monomers for the preparation of polyamides. Preparation of an L-arabinitol-based polyamide.

Dihydrochlorides of 1,5-diamino-1,5-dideoxy-2,3,4-tri-O-methyl-L-arabinitol (and xylitol) and pentachlorophenyl esters of 2,3,4-tri-O-methyl-L-arabinaric (and xylaric) acids have been prepared as suitable bifunctional monomers for linear polycondensations. A new aregic AABB-type L-arabinitol-based polyamide is also described from the corresponding monomers. It was crystalline with T(m) 250 degrees C, optically active, and soluble in the usual organic solvents, including chloroform, and in water. Its M(w) obtained by GPC was 27,500 with a polydispersity of 1.4.